Study of recovery and first recrystallisation kinetics in CGO Fe3%Si steels using misorientation‐derived parameters (EBSD)

Abstract

Summary Many metallurgical processes produce characteristic dislocation accumulation, with heterogeneous spatial and orientation distributions and further development of microstructures after heat treatment. Recovery and recrystallisation behaviours are direct consequences of those uneven dislocation distributions. The Electron BackScatter Diffraction (EBSD) technique can be used for the characterisation of such microstructural features, including: Density of Geometrically Necessary Dislocations (GND), Kernel Average Misorientations (KAM), Grain Orientation Spread (GOS), Grain Average Misorientation (GAM), Grain Reference Orientation Deviation (GROD – Angle) and GOS/D, where D is an assumed characteristic grain length. Production of Fe3%Si alloys with a Goss texture, essential step in the manufacture of electrical transformers, requires several different processing stages, including the one called primary recrystallisation, a key process preceding abnormal grain growth. The structure of grains and different microstructural aspects of the recrystallisation stage will provide the conditions for development of the Goss orientation during abnormal grain growth. In the present work we use GOS, GAM, GROD, GOS/D, GND and KAM, calculated from EBSD scans performed on cold rolled Fe3%Si alloys subject to increasing heat treatment times, to characterise the kinetics of recovery and primary recrystallisation in an Fe3%Si alloy. Difficulties in the interpretation of these results may arise from the interactive competition between various microstructural features. Hardness measurements were also performed in order to validate recovery and recrystallisation evolution by classical methods. It was found that the global GOS (i.e. including grains of all orientations) shows changes which can be related to those observed in the hardness for high annealing temperatures but it is not sensitive to microstructure evolution occurring at low temperatures. Meanwhile, GND undergoes changes at all annealing temperatures and, remarkably, it responds to the recovery that GOS cannot detect at low temperatures. The GAM parameter seems to follow better the microhardness results. When grains belonging to different texture components are analysed, gamma fibre grains are the first to recrystallise and alpha fibre grains the last. Lay Description Many metallurgical processes produce characteristic dislocation accumulation, with heterogeneous spatial and orientation distributions. Further development of such microstructures occurs with subsequent heat treatments. Recovery and recrystallisation behaviours are directly affected by consequences of those uneven dislocation distributions. The Electron Back Scatter Diffraction (EBSD) technique can be used for the characterisation of such microstructural features using different magnitudes that describe locally or globally misorientations between various locations in the material. In search of the best parameters [among them: Density of Geometrically Necessary Dislocations (GND), Kernel Average Misorientatio...

EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy

“…In a polycrystalline texture, the relative difference in crystallographic orientation between two neighbouring grains is called 'Misorientation', a local transformation in the crystallographic frame [46,47]. In coordinate systems, misorientation is described as the rotating of two grains with regards to their respective crystallographic directions.…”

Microstructural Study of a Mg–Zn–Zr Alloy Hot Compressed at a High Strain Rate

“…It is noted that the DRXed grains formed by CDRX or DDRX via grain boundary corrugation/bulging tend to have orientations similar to the parent grains [34,35]. The grain reference orientation deviation (GROD) map [29,36] for α-Mg grains is shown in Figure 12b. It is suggested that the Zr-rich coarse grain had substantial misorientations built up in the vicinity of boundaries, which supports the assumption that CDRX and DDRX were active in these regions [33].…”